Fix for buggy splash screen [verified on HP Compaq 6715b]

I understand that a buggy splash screen is a fairly common problem in Ubuntu and Trisquel.

While I am sure that there are a lot of different causes for this, one cause is that it makes assumptions about default graphics states that aren't true because Grub has changed the graphics state. (This is the case on an HP Compaq 6715b)

This can be resolved by setting the line GRUB_TERMINAL=console in /etc/default/grub, then running update-grub. This is fine since the Grub menu is hidden anyway.

This will limit Grub to a 24x80 text terminal, rather than a graphical display.